LDMOS transistors as inverters

Discussion in 'The Projects Forum' started by Tako, Oct 21, 2014.

  1. Tako

    Thread Starter New Member

    Oct 21, 2014
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    Hello,

    I have the following question: is it possible to construct an inverter using LDMOS transistors when HV power supply is equal to 30 V and maximum VGS for LDMOS transistors is 5 V? Moreover, lower MV domain is 5 V.

    See the attachment for visualization - problem section.

    I can do following solution - see the attachment (solution section). However, doing it means constant current consumption and problems to turn on PMOS (apply 25 V on its gate). PMOS is turned on through 5R resistor.

    Do you know if it is possible to construct such an inverter?

    LDMOS inverter - full.png
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    You could use a BJT transistor as a level-shifter to drive the gate.
     
    Last edited: Oct 21, 2014
  3. Tako

    Thread Starter New Member

    Oct 21, 2014
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    How do you imagine to do it?
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Something like this:
    LevelShift.gif
     
    Tako likes this.
  5. Tako

    Thread Starter New Member

    Oct 21, 2014
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    I see. However I have some remarks to your solution:

    1. high state on the gate of PMOS transistors is obtained through 3k3 resistor. The time to obtain the high state is slowed down. This time is longer than in the solution proposed by me where high state is obtained through switch.
    2. there is still power consumption for the low state (when bjt is on) and low state on the gate of PMOS transistor is obtained through 22k resistor. Thus this solution is the same as the one proposed by me.

    Any other modifications / propositions?
     
  6. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Isn't this what half bridge mosfet gate drivers do?
     
  7. Tako

    Thread Starter New Member

    Oct 21, 2014
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    You mean that:

    [​IMG]

    ?

    I'm curious how to do a level converter in my example using the solution from the picture above. I must leave the computer now, but I think I have an idea.

    One remark: my problem / solution should be implemented as integrated circuit, NOT a discrete solution.
     
  8. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Kind of like your attachment, but without the optocoupler. I have another question for you about your circuit. Why are you using both a logic level and standard mosfet? There are logic level mosfets that will handle the 30V and switch with 5V.
     
  9. Tako

    Thread Starter New Member

    Oct 21, 2014
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    If the picture is what you meant (I understand that without optocoupler - it was just the first picture that I found) then please tell me how to make level shift while there is only 30 V and 5 V power domains. Level shift should give 25 - 30 V.

    In my technology there is 5V domain where you have mosfets that operate normally, what means that they can handle VGS and VDS maximum voltages equal to 5 V. Then you have LDMOS transistors that can handle VDS = 30 V, but VGS = 5V only.
     
  10. Tako

    Thread Starter New Member

    Oct 21, 2014
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    Ok, the best solution for now is the one proposed by Alec_t - put additional switch into my solution for the resistor divider. There is still power consumption for output state high. Time to turn PMOS and power consumption through resistor divider is the trade-off.

    Thanks for discussion. :)
     
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